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Screen Printing Adhesive on Mixed Technology Boards

John S

#18181

Screen Printing Adhesive on Mixed Technology Boards | 15 November, 2001

My company is in the process of evaluating dispensing/screen printing vendors for a new production line that will build a mixed through hole and smt board in high volume. DEK recently came out with a system that uses a thick plastic stecil with machined out pockets to print adhesive on the wave solder side of a board with through hole parts. Has anyone had experience with this process? How does it compare to dispensing? Are the stencils difficult to keep clean (during and after production)? We'll be printing on a HASL finished board, should it seal well enough to the stencil?

Thanks John S

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#18185

Screen Printing Adhesive on Mixed Technology Boards | 15 November, 2001

John, To answer your question, we have a number of customers that are using this process, Pumpprinting very successfully! If you would like to contact myself I can provide you with some very good references that will be able to answer all your questions. I can tell you that the cycle time is typically less than 30 secs per board no matter if it is 1000 or 10,000 dots that need to be put down. The cleaning of the stencils is a matter of contacting your adhesive material supplier and finding one that will work in your cleaner. In fact we have a some customers that are using their cleaner for both the paste and the adhesive stencils with no problems reported. As for HASL boards, our customers currently find no issue with using this type of finish on the boards.

Please feel free to contact myself or any of the other Applications Engineers to discuss your process more in detail.

Jerry Hingtgen Applications Eng, DEK USA 908-782-4140

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Mr.T

#18187

Screen Printing Adhesive on Mixed Technology Boards | 16 November, 2001

John,

I have seen process mixed technology in customer site.Now they dont use wave but they print paste through hole components.It is good and fast but it did take a time when they found a right paste to do that.Stencil is plastic and aprox.3mm(3000um)thick.If you go that way it will not be easy to find a right solderpaste. Regards, MDR

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Verm

#18188

Screen Printing Adhesive on Mixed Technology Boards | 16 November, 2001

John where in the world are you based?

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#18204

Screen Printing Adhesive on Mixed Technology Boards | 19 November, 2001

Printing paste with an �approx. 3mm (3000um) thick� stencil!!! Shirley, you jest!!!

Please help us understand this better.

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#18205

Screen Printing Adhesive on Mixed Technology Boards | 19 November, 2001

HAS ANYONE HAD EXPERIENCE WITH THIS PROCESS? => We print glue with a thick stencil on one product. Although it works �correctly�, we don�t like it because the process flow is goofy. So on a high mix line, it ends-up being a burden.

Also, there is no rocket science behind making the stencils for this process.

We are not experts in this, but we feel that it is difficult to control glue release. The issues appear to be: * High aspect ratio. * Curing of glue through the production run.

HOW DOES IT COMPARE TO DISPENSING? => It is way: * Cheaper from a capital expense stand-point * Faster board mateial deposition cycle time * Less controlable * Slower turn job turns [but that probably doesn't matter because your P&P will be the long pole] * Lower flexibility [but that probably doesn't matter because you're setting this line for a particular product]

Search the fine SMTnet Archives for a comparison of using a dispenser and a printer to deposit paste. [Even though you're doing glue, many of the points of comparison carry through.]

ARE THE STENCILS DIFFICULT TO CLEAN? No, if you don�t let the glue cure, as with metal glue stencils.

SHOULD THE HASL BOARD SEAL WELL ENOUGH TO THE STENCIL? Yes

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John S

#18210

Screen Printing Adhesive on Mixed Technology Boards | 20 November, 2001

Dave,

How do you try to contol the glue release? The information we've gathered so far indicates that this is controlled by the speed and distance of stencil separation. How do your defect levels compare to dispensed products?

Thanks again, John S

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#18216

Screen Printing Adhesive on Mixed Technology Boards | 20 November, 2001

You�re correct. The release characteristics of epoxy differ from solder paste. Consider: * Using print/flood stroke, on-contact print cycle. * Printing slow enough to fill the hole with adhesive. * Overcoming the thixotropic [The viscosity of thixotropic gels decreases when stressed.] qualities of the adhesive to get it to release from the long walls of the stencil. * Keeping aspect ratios less than 3:1.

If process time and product suitability are the driving factors, I would (begrudgingly) print epoxy. Since you are setting-up a production line for this product, I assume you expect to run a large volume of product.

We have never compared the defect levels of dispensing and printing. The comments made earlier, may be worth repeating:

Factor||Dispenser||Printer Deposition control||High control over amount ||Difficult to control amount ||||Stepped stencils can be a nightmare ||||Stencil apertures clog ||Coplaniarilty issues controllable ||Coplaniarity issues make printing difficult ||Gel rheology does not play a large role in dispensing||Rheology requires constant working of gel ||Requires process control to prevent missing dots||Requires process control to prevent misprints, clogged apertures

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Scott Davies

#18253

Screen Printing Adhesive on Mixed Technology Boards | 26 November, 2001

We've used pump print stencils on and off for a couple of years now, and experimented with various epoxies. One supplier gave us some samples to try and we found that the adhesive they supply for normal metal stencil printing didn't work well with the thicker plastic stencil. However, we found quite by accident that a product they had developed specifically for pin transfer application worked perfectly with the pump print process.

Even so, the main problems concerning pump printing remain cleaning and keeping clean the stencil after and between uses, and the amount of adhesive which gets wasted and thrown away at the end of the run.

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#18258

Screen Printing Adhesive on Mixed Technology Boards | 26 November, 2001

To all, For the benefit of everyone there will be a session conducted at APEX on this topic. I have included the information that I pasted from the APEX website (http://www.goapex.org).

ADHESIVE PRINTING Chris Marinelli, Loctite

Tuesday, January 22 1:30 pm-3:00 pm

This session deals with screen printing of adhesive for component attachment prior to wave soldering. Stencil design and print performance for thick plastic stencils and thick metal stencils with and without relief pockets, for clinched leads of axials and radials inserted from the other side of the board will be presented. Glue properties and their influence on glue height and volume as well as effective glue stencil cleaning will also be discussed.

Metal Stencils for Adhesive Printing Bill Coleman, Ph.D., Photo Stencil Inc.

Optimizing the Print Performance of SMT Adhesives Rick Lathrop, Heraeus

Adhesive Cleaning Bill Schreiber, Smart Sonic Stencil Cleaning Systems

Depositing Thirty Million Glue Dots Per Hour Jerry Hingtgen, DEK USA, Inc

If you are unable to attend it will be published in the proceedings.

Regards,

Jerry Hingtgen

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